Re: [exim] MX for Multiple Domains using Exim4 as smarthost

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Author: Jason_Meers
Date:  
To: Wes Carver
CC: exim-users
Subject: Re: [exim] MX for Multiple Domains using Exim4 as smarthost
Wes Carver wrote:
> I have an Exchange server that I use to host 3 domains for our
> organization. (I wonder how many users stopped reading there.)
> I have set up a Debian box with Exim to act as a smarthost. (Please do not
> send me to the Debian users group. This is not a question about the Debian
> setup.)
>
> I can successfully send mail out of our network, and I can send email from
> one domain to another on the inside of my network. I am trying to set up
> the MX records/reverse DNS records with our ISP/Domain registrar.
>
> I am unsure of how to proceed because my smarthost is the server that
> receives the email on the edge of my network for all of our domains.
>
> My Exchange server looks like gcmmail01.domain1.com, gcmmail01.domain2.com,
> and gcmmail01.domain3.com when I send the mail. I have set up host records
> with these names for the external IP for each. I have set up a reverse dns
> record for each also.
>
> I can not connect to my server from the outside. At this point, I don't
> know if it is the settings on my edge router, or some problem with the Helo
> because of the way I set up the MX records.
>
>

Which server can you not connect too?

> To be honest, I think it might be a little of both.
>
> Is it OK that the MX record points to a server that has a different FQDN?
> The server is not named gcmmail01.domain1.com, or gcmmail01.domain2.com or
> gcmmail01.domain3.com? The records point to IPs that NAT to
> MailGateway.domain1.com (the smarthost).
>
> I have set up servers to point to a smarthost, but this is the first
> smarthost I have configured.
>

I'm not sure that I have understood your description correctly but if
you are explaining a situation where you have 3 exchange servers on the
LAN (or 1 exchange server that handles 3 domains) and an exim box that
is in the dmz (or on the LAN but publicly accessible via NAT) then you
should just be able to use the exim box as a smarthost for all inbound
and outbound mail.

In this instance your MX records will all point to the exim box which
will have each of the 3 domains used by exchange setup as relay domains,
and your exchange servers will have your exim box setup as their
outbound smarthost.

Deliveries in both directions can be done via "literal" ip addresses, so
MX records need only be concerned with getting inbound messages routed
to exim first (from the outside world).

If this is the case then please see the following paper (and sample
config files) here:
http://www.exim-new-users.co.uk/content/view/95/39/

If this is not the case then I would still suggest reading the first
half of the paper which deals with some of the security implications of
presenting an exchange server directly to the Internet.

Regarding the server that you cannot connect to, see the following
troubleshooting sections in the paper:
- Test SMTP connectivity from Exim to Exchange -
- Test SMTP connectivity from Exchange to Exim -
- Test SMTP Relay from Exim to Exchange -
- Test SMTP Relay from Exchange to Exim -

Thanks
Jason_Meers
--
http://www.exim-new-users.co.uk